Parviz Soroushian

Distribution and Orientation of Fibers in Steel Fiber Reinforced Concrete

Measurements were made on the number of fibers per unit cross-sectional area in steel fiber reinforced concrete specimens incorporating various volume fractions of fibers of different types. Based on statistical evaluation of the measured values, the differences in fiber concentrations at different locations on the cross section were assessed. Theoretical expressions were derived for the number of fibers per unit cross-sectional area in fiber reinforced concrete, with due consideration given to the effects of the surrounding boundaries. The effects of vibration on reorientation of steel fibers in concrete were investigated through comparisons betwen the computed and measured values of number of fibers per unit cross-sectional area.

Mechanical properties of polypropylene fiber reinforced concrete and the effects of pozzolanic materials

Abstract A comprehensive set of experimental data were generated regarding the effects of collated fibrillated polypropylene fibers at relatively low volume fractions (below 0.3%) on the compressive, flexural and impact properties of concrete materials with different binder compositions. Statistical analysis of results produced reliable conclusions on the mechanical properties of polypropylene fiber reinforced, concrete and also on the interaction of fibers and pozzolanic admixtures in deciding these properties. Polypropylene fibers were observed to have no statistically significant effects on compressive or flexural strength of concrete, while flexural toughness and impact resistance showed an increase in the presence of polypropylene fibers. Positive interactions were also detected between fibers and pozzolans.

STRENGTHS OF RECYCLED AGGREGATE CONCRETE MADE USING FIELD-DEMOLISHED CONCRETE AS AGGREGATE

Experimental work was conducted to determine the compressive, splitting tensile, and flexural strengths of recycled coarse aggregate concrete and to compare them with those of concrete made using natural crushed stone. The properties of the aggregate were also compared. The fine aggregate for recycled and conventional concrete was 100 percent natural sand. Two sources of recycled aggregate and one source of natural aggregate were used. Two maximum sizes of aggregates, two levels of water-cement ratio, and two levels of dry mixing time of coarse aggregate were chosen to perform the experiments based on a full-factorial design. Test results indicate that the strength characteristics of recycled aggregate concrete are influenced by key factors, such as the strength of the original concrete, the ratio of coarse to fine aggregate in the original concrete, the ratio of top size of aggregate in the original concrete to that of the recycled aggregate, and the Los Angeles abrasion loss and water absorption of recycled aggregate. These factors also influence the effect of water-cement ratio, aggregate top size, and dry mixing on the strength characteristics of recycled aggregate concrete. It is also shown that the conventional relationships between splitting tensile, flexural, and compressive strengths may have to be modified for recycled aggregate concrete. The final conclusion is that through proper measures high-quality concrete materials can be produced using recycled concrete aggregate. For this purpose, it is necessary to determine the properties of the original concrete, based on which realistic qualities can be targeted for recycled aggregate concrete.

FIBER-TYPE EFFECTS ON THE PERFORMANCE OF STEEL FIBER REINFORCED CONCRETE

The paper reports the results of an experimental study on the relative effectiveness of different types of steel fiber in concrete. A constant fiber volume fraction of 2 % was used throughout this investigation. The fresh fibrous mixes were characterized by their slump, inverted slump-cone time, and subjective workability, and the hardened materials by their compressive and flexural load-deformation relationships. The overall workability of fresh fibrous mixes was found to be largely independent of the fiber type, with crimped fibers producing only slightly higher slumps. Hooked fibers were found to be more effective than straight and crimped ones in enhancing the flexural and compressive behavior of concrete. Under flexural loads, crimped fibers were slightly less effective than straight ones in improving the strength and energy absorption of concrete.

Control of Plastic Shrinkage Cracking with Specialty Cellulose Fibers

Specialty cellulose fibers processed for the reinforcement of concrete offer relatively high levels of elastic modulus and bond strength. The hydrophilic surfaces of cellulose fibers facilitate their dispersion and bonding in concrete. Cellulose fibers have small effective diameters that are comparable to the cement particle size, and thus promote close packing and development of a dense bulk and interface microstructure in the matrix. The relatively high surface area and the close spacing of cellulose fibers when combined with their desirable mechanical characteristics make them quite effective in the suppression and stabilization of microcracks in the concrete matrix. The investigation reported concerns the effects of specialty cellulose fibers on the restrained plastic shrinkage cracking of conventional and high-performance concrete. Cellulose fibers were used at 0.06% volume fraction, which is equivalent to a fiber content of 0.9 kg/cu m (1.5 lb/cu yd). Plastic shrinkage cracks occur when the early-age shrinkage movements (prior to final set) are restrained; this commonly occurs on the surfaces of concrete flatwork in windy, hot, and dry conditions that promote rapid evaporation. Under such conditions, a moisture gradient develops in concrete that produces internal restraint against shrinkage movements of the surface layers. In the experimental program on restrained shrinkage cracking of conventional and high-performance concrete, noting that plastic shrinkage cracking test results show an inherently high variability, statistical analysis of replicated test results confirmed that cellulose fibers are effective in reducing the plastic shrinkage cracking of conventional and high-performance concrete. Cellulose fibers had statistically comparable effects on plastic shrinkage cracking of conventional and high-performance concrete.

Dispersion of plant pulp in concrete and use thereof

Pulp fibers derived from wood or non-wood plants or recycled paper products, which are about 0.1-30 mm long and about 0.001-0.1 mm in diameter with length-to-diameter ratio of about 30-3000, are dispersed in conventional concrete mixtures using conventional mixing equipment for effectively improving fresh and hardened concrete properties at relatively low cost. Dispersion is achieved by individualizing the plant pulp fibers so that they are not fully bonded to each other, and dispersing the individual fibers in concrete at relatively low dosages of about 0.3-30 kg per cubic meter. Once individualized, the affinity of plant pulp fibers for water facilitates their dispersion in conventional concrete mixtures. Fresh concrete mixtures incorporating the dispersed individualized plant pulp fibers possess desirable workability, resistance to segregation and bleeding, pumpability, finishability, and reduced rebound when pneumatically applied. Hardened concrete materials incorporating the dispersed individualized plant pulp fibers provide improved crack resistance, toughness characteristics, impact resistance, fatigue life, abrasion resistance, and other mechanical, physical and durability characteristics. Precast and cast-in-pace concrete as well as plain and reinforced concrete and shotcrete benefit from such improvements in fresh and hardened material properties rendered by dispersed plant pulp fibers.

Bond of Deformed Bars to Concrete: Effects of Confinement and Strength of Concrete

Slippage of the beam reinforcement at beam-column connections is an important cause of damage to reinforced concrete frames under static and dynamic loads. This paper summarizes the results of an experimental study on the effects of confinement and compressive strength of concrete on the local bond stress-slip characteristics of deformed bars. The test data indicate that, as far as the bond-splitting cracks are restrained by reinforcing bars crossing these cracks, confinement of concrete has insignificant effects on the local bond behavior. The ultimate bond strength, however, increases proportionally with the square root of concrete compressive strength. An empirical model was develped for local bond stress-slip relationship of deformed bars in confined concrete.

ASSESSMENT OF REINFORCING EFFECTS OF RECYCLED PLASTIC AND PAPER IN CONCRETE

In this research, mixed plastic and paper waste products were subjected to various processing schemes that yielded end products of different slenderness and fineness levels. These end products were evaluated as discrete reinforcement systems in concrete. The dosages of recycled products were adjusted in light of their geometric attributes to yield fresh concrete mixtures with desirable workability, homogeneity, and air content. The effects of discrete reinforcement systems of recycled and virgin origins on concrete mechanical, physical, and durability properties were examined. Results indicate that discrete reinforcement systems derived from abundantly available waste streams can, at proper amounts, yield positive reinforcing effects in concrete. Improvements in restrained shrinkage crack control and impact resistance were particularly significant and comparable to those of virgin fibers.

MECHANICAL PROPERTIES OF CONCRETE MATERIALS REINFORCED WITH POLYPROPYLENE OR POLYETHYLENE FIBERS

An experimental study was conducted to compare the effectiveness of fibrillated polypropylene and high-modulus polyethylene fibers, both used at relatively low volume fractions, in enhancing the mechanical properties of concrete materials. Replicated flexure, impact, and compression tests were conducted, and the results were analyzed statistically. It was concluded that lower volume fractions of high-modulus polyethylene fibers can produce flexural and impact strengths comparable with those obtained at 0.1% volume fraction of fibrillated polypropylene fibers.

LOCAL BOND OF DEFORMED BARS WITH DIFFERENT DIAMETERS IN CONFINED CONCRETE

Slippage of the beam reinforcement crossing the interior joints in reinforced concrete frames can lead to large fixed-end rotations and overall beam deformations, causing major structural damage under severe seismic excitations. It is thus important to anchor adequately deformed bars inside the confined core of earthquake-resistant joints. The key factor governing the anchored-bar behavior in confined concrete is the local bond stress-slip relationship. This investigation addreses the effects of bar diameter on this relationship. Experimental data have been generated on the local bond behaviour for deformed bars of different diameters partially embedded in confined concrete. The results are used to assess the anchored bar-diameter effects of the ultimate local bond strenth and local bond stress-slip relationship in confined concrete. Based on the test data, an empirical local bond constitutive model has been generated that accounts for the bar diameter effects.